Widely spread is a technique to form a thin film on a semiconductor, electronic part, ornamental part, etc., by means of a sputtering apparatus using a sputtering source in which a magnet is placed on the rear surface of a target. In such a sputtering apparatus, an inert gas, for example, Ar, serving as a discharging gas, is introduced in a vacuum chamber. A sputtering source is arranged in the vacuum chamber. A negative voltage is applied to the sputtering source, thereby generating magnetron discharge and ionizing the discharging gas introduced in the vacuum chamber. The ionized argon positive ions are accelerated and collided with the target surface of the sputtering source, so that the target surface is sputter-evaporated. The sputter particles are deposited on a substrate, thereby forming a thin film made of the material of the target. This is called sputtering.
During the process of sputtering, the magnetron discharge may be changed to arc discharge. If magnetron discharge is shifted to arc discharge, sputtering cannot be performed.
Therefore, immediately after the arc discharge occurs, a reverse voltage pulse, which maintains the target at a positive potential, is slightly applied, so that occurrence of arc discharge is suppressed.
To prevent the aforementioned arc discharge, the following preventive measures have conventionally been taken:
(1) to insert a stabilizing resistor or a choke coil in serial with a load; PA1 (2) to use an intermittent DC power source; PA1 (3) to insert a choke coil for limiting a current, a resonating reactor and a capacitor between the DC power source and the load and apply a reverse voltage with vibration of a voltage and a current which are generated at the arc discharge, so that the arc discharge can be stopped; PA1 (4) to clamp the reverse voltage described in (3) to stop the arc discharge in the reverse direction, thereby preventing the arc discharge more securely; PA1 (5) to detect arc discharge and stop the output of the DC power source for a certain period of time; PA1 (6) to detect arc discharge and apply a reverse voltage to the load for a certain period of time; and PA1 (7) to apply a reverse voltage to the load at regular intervals regardless of whether arc discharge is detected. PA1 (1) as the pressure is lowered, vibration of the discharge voltage and current occur, resulting in that the magnetron discharge is stopped; PA1 (2) the arc discharge occurs, resulting in the stop of magnetron discharge; etc.
However, when the stabilizing resistor is inserted in parallel with the load in the circuit of (1), the resistor consumes a large amount of power and a sputtering power source of high power cannot be produced. Further, in the case of the choke coil, generally, the circuit of (3) has been made by parasitic elements (L, C) of the wire. This case has a problem that the discharge voltage and current vibrate due to the negative characteristic of the DC sputtering discharge.
Further, the circuit of (2) has a problem that control of the arc discharge is too late. Since the first side of the transformer is controlled by SCR and the second side is merely rectified by a diode, the sputtering discharge is intermitted at the frequency of an AC line, and the period of time between the occurrence and the extinction of arc discharge corresponds to the firing angle of the SCR. Thus, there is a problem that the arc discharge control delays.
Furthermore, the circuits of (3) to (7) have the following problem. When sputtering is performed under a gas pressure lower than the discharge start pressure, the DC sputtering discharge characteristic is of negative characteristic and the discharge voltage and current vibrate. This is because there is no stable point with respect to the negative resistance characteristic, since the power source characteristic from the viewpoint of load is not a constant current characteristic. The reason for vibration is that a smoothing capacitor is inserted in an output of the DC power source.
The discharge phenomenon has various hystereses. The hystereses include a discharge start voltage and a discharge voltage, and a discharge start pressure and a discharge stop pressure. When the discharge stop pressure is measured, it is impossible to obtain data as good reproducibility as that of the start pressure. When the cause was investigated, it was discovered that the magnetron discharge was stopped at a pressure lower than the discharge start pressure in the following cases:
In other words, it was discovered that, since the magnetron discharge was stopped due to not only the characteristics of the magnetron sputter source, but also the vibration of the discharge voltage and current and the arc discharge, reproducibility of the discharge stop pressure could not be obtained.
As described above, with the conventional measures to cope with arc discharge, stable sputtering could not be performed at a pressure lower than the discharge start pressure.